INDIVIDUAL SECTORS - Proceedings of the Workshop on Energy Demand

Electricity and Energy Savings in Industry J. Bouchet

It may seem astonishing to hear stated that the use of

electrical processes in industry could lead to savings of primary energy.

It is known that the development of nuclear energy may save considerable amounts of hydrocarbons. However, it is generally believed that the transformation of hydrocarbons into electricity may reduce the efficiency of primary fuel utilization to as little as 35% of its potential. Comparisons of primary fuel

utilization for electricity with conversion of thermal into

mechanical energy, do overlook the fact that losses are low in the actual use of electricity.

Thus with conventional fuels, losses are moderate during production--as for instance in industrial steam generators--while they are high in distribution and, above all, in use. For example, a survey conducted in 1970 in the Federal Republic of Germany showed that out of an overall consumption of 313 Mtec,' 210 Mtec were

sheer loss and only 103 were real corisumption; hence the overall efficiency came to no more than 33%. True, the enquiry bore on all energy users and not only on industrial consumers, but the lowest efficiencies are not always found in the industrial field.

This raises the question whether the efficiency in the use of electricity-consuming processes can be.sufficiently high to

counterbalance the initial disadvantage of this type 05 energy?

Could this be possible on account of the wide variety of forms in which it may be used: Joule effect, Peltier effect, induction, electric arc, radiation (light, radio-electrical, infrared, ultra- violet, high frequency, hyperfrequency, etc.), electronic heating, magnetic field, electrical field, electrolysis, plasma and so on.

'Mtec = million (metric) tonnes coal equivalent.

This variety and ease of control enable electric energy to be supplied where, as, when and how it is wanted. One may even give up supplying heat from the outside and have it nascent inside the product itself, as for instance by induction, by the Joule effect, by hyperfrequency, by friction, etc. For one can engender heat inside a liquid by friction, as for instance during ultra- fast sterilization; in a few tenths of a second, milk or fruit

juice can be heated by means of a metal disk rotating rapidly inside a container with very little play between disk and container.

Are we sufficiently aware of the hopes now arising from current research on separation and concentration processes in membranes by reverse osmosis, or ultra-filtration, by means of mechanical

energy of which the form most economical in primary energy is still the electric motor? For example, the treatment of one cubic meter of lactoserum through membranes to recover the protein requires only six kg of fuel oil equivalent, against twenty-five kg in a conventional evaporator. Also in the field of protein recovery, an experimental mechanical pressing of lucerne conducted in 1973 to reduce its water content from 90% to 50% (before processing it in an oven), used only seventeen KWh, equivalent to four kg of fuel oil, against twenty kg in a conventional oven to arrive at the same reduction of water content.

Further examples are: the numerous uses of heat pumps; the drying of polymerisable inks by ultra-violet rays; and the residual waters treatment by electroflotation and electro-flocculation.

Innovations will invade more and more industries. Thus in organic electrochemistry, recourse to the action of electrons and protons inside molecules is envisaged: it could, for instance, lead to oxido-reduction reactions by means of brush discharges. Research in this is under way with collaboration between C N R S ~ and EDF. 3 No wonder that, in such a framework, energy savings may be spectacu-

lar the moment one does not merely replace flames by resistors, but one has an entirely novel process through electricity.

2 ~ e n t r e National de la Recherche Scientifique (France)

.

3~lectricit6 de France

But is there a way of assessing impartially the potential energy savings related to a given process? In the present economic and industrial context, moreover, can one be concerned solely with the concept of apparent savings in energy, without at least associa- ting it to the concept of savings in raw materials?

Before coming to some more detailed--though as yet incomplete-- examples of savings in primary energy by substituting new electrical processes for conventional ones, it is necessary to stress the points that the concepts of savings in energy and in raw materials--

possibly even in labor and foreign currency--cannot be dissociated

and that it is difficult to accurately assess the overall energy savings.

This may be seen in the following example: Take two processes, both of them designed to melt aluminium, the first through a flame fur- nace, the second through a resistor oven, to make molded pieces.

It requires about 1,500 thermies4 of fuel per metric ton of aluminium in a flame furnace to match the 600 kWh required by the electrical process.

If electricity comes from an oil-fired power plant, it will yield about 2.5 thermies per kwh. Thus both processes seem to be equivalent in terms of primary energy (1,500 thermies).

Let us go deeper into the matter: the first process may entail an additional loss by fire of 0.7% of the metal which is reduced from 1.4% to 0.7% in an electric furnace. To be valid, the comparison should entail the same amount of finished product.

Naturally the additional 0.7% of thermies used in heating must be taken into account, but these ten thermies are negligible.

The point is that we have to produce the additional seven kg of aluminium. This needs, starting from the crude bauxite, an extra 50,000 thermies of energy--mechanical, thermal, electrical-- per metric ton of metal, that is to say 350 thermies to arrive .at

',he th/t/Oc (thermie/tonne/degree C) = 1,000 kilocalories/metric tonldeqree C = 2,240 BTU/long ton OF.

the seven kg required to make up for losses by fire. In this way one will expend 1,850 thermies per metric ton in the flame furnace against 1,500 thermies in an induction furnace. This

will deeply modify an initial conclusion drawn from too limited an analysis of apparent savings.

Even leaving aside the economic aspect of saving foreign

currency, or even labor, at least two objections may come into mind.

They are: first, is not the reasoning incomplete by not taking into consideration the potential heat recovered downstream from the furnace? Second, is not this example too biased in favor of

electricity, hence not generalizable?

To the first objection there can be a simple reply: the re- covery possibilities must be carefully examined, because they can be very different. So, when replacing a flame furnace by an induc- tion furnace, it may even be that recovery by cooling water from the coils is sometimes easier--and more profitable--than recovering the heat from smoke effluent, especially when reusing the heat for space heating (for one among the many problems of recwering down- graded heat is indeed to find the right needs close by: they must be of the same order of magnitude as the source, both in quantity of heat and in temperature level).

To the second objection--bias in favor of electricity--one could answer that this example is not the only one currently avail- able, if one considers all of the fields of applications, for example :

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Thermocuring of concrete by electricity instead of by steam or hot water saves about 65% of primary energy, bringing the average consumption to forty-five liters of fuel oil per cubic meter of concrete (i.e. 450 th/m 3 ) against sixty kwh per cubic meter (i.e. 150 tn/m 3 )

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Drying of maize by dehydration with heat pump consumes twelve ktih per quintal, i.e. about 3.5 liters of fuel oil against 5.5 liters with a flame dryer;

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Wood drying by a similar process saves almost 50% of the primarj

energy by cutting downthe amount of fuel oil used from some forty liters per m3 of dried wood, plus twenty-five kWh for ventilation (i.e. 460 th/m3) instead of 100 kWh/m3 (i-e.

250 th/m 3 1 ;

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Reheating the temperature holding before forming of annealed steel billets in ovens producing a few tons per hour by means of conduction heaters entails a saving of 20% to 40%

Thus 1,300 thermies per metric ton consumed with conventional heating--including an additional 1.5% loss by fire--is brought down to 410 kwh (1,025 thermies) in an induction furnace and 300 kwh (750 thermies) in a conduction heater.

The basic question, however, remains: how to assess validly

and impartially the energy savings involved in one of the two processes?

Perhaps the few examples mentioned may have foreshadowed an answer.

First, an analysis must start from a common point in the two processes and end up with equal quantities of products able to give the same service. For instance, when reheating steel billets in order to make rods, calculations must begin in both cases with cold billets and end up with the same weight of rods of the same quality.

This is a relatively simple case, requiring only that one takes into account the energy available in the fuel, plus any supplemental consumption (which is often neglected), such as ventilation, or more generally motive force, minus the recovery of any potential heat.

Another thing (which is often omitted) is to take into account the difference in losses by fire in terms of primary energy. This quanti- fication of loss by fire must generally begin at the iron ore

extraction phase (though in some cases it may be possible to recover calamine). Lastly it is necessary to convert the kWh into units or primary energy. This is one of the simplest examples to be found when the energy substitution is done by means of electricity.

But it is already far more complex if compared with the relative simplicity of substituting a gas flame for a fuel oil flame, although differences in the nature of their radiation may bring some problems regarding a correct appraisal of efficiencies. It is, however, im-

p o s s i b l e t o n e g l e c t some f a c t o r s t h a t s h o u l d b e m e n t i o n e d :

As things stand, in Europe and more particularly in France, a coefficient as high as 2.4 or 2.5 th per kwh6 will soon grow obsolete due to the massive arrival of nuclear power. Indeed, when the population of conventional thermal plants and nuclear plants has been reoptimized in terms of their respective operating costs, the conventional plants will operate for no longer than about 2,000 to 3,000 hours per annum. And their operating periods during peak hours will be virtually independent of the amount of regular consumption by the industrial users of electricity. It will then happen that virtually all of the industrial development of

electricity will be based on nuclear energy. In France this will come about 1985, when the proportion of nuclear in the marginal kwh output will have risen from around OX in 1980 to almost 100% in 1985.

There is a difficulty in determining a valid equivalent of n~clear energy in terms of primary energy. A simple and often re- peated reasoning holds that since nuclear energy may be used either in the form of a hot fluid (e.g. stream), or in the form of electricity one has to penalize electricity by the efficiency factor of the

conversion of heat into mechanical energy, so the equivalence factor could be something like 0.86 x 3 = 2.5.

But is this reasoning really similar to that generally used for liquid and gas fuels? In such cases the energy they develop during complete combustion is generzlly referred to. Logically, one should have to consider the theoretical heat given off by the fission of uranium 235. If the phenomenon merely involved the com- plete disappearance of the uranium, the situation would be similar

6 ~ o n f usion is to be avoided between the equivalence factor in terms of primary energy with what might be called the coefficient of energy substitution. Thus in an above example, namely the pres- sing of lucerne, in which seventeen kWh were used instead of twenty kg of fuel oil (200 th), the substitution coefficient would reach 11.5 thermies per kWh. As opposed to the equivalence factor in primary energy (related only to the mode of electricity production), the substitution coefficient (related only to both the modes of using electricity and of using fuels in the considered processes) is all the more favorable to electricity as it is large.

to the disappearance of some conventional fuel; but in this case a new fuel is simultaneously generated from uranium 238 in

quantities which may even exceed those destroyed by fission. So what could be the consumption of primary energy to be validly assigned to breeder reactors, other than possibly a negative con- sumpt ion?

Without fully answering this question, it may be said that in energy balance sheets drawn up for facilities still operative in the 1985's, a coefficient of some 2.5 thermies per kwh will be pessimistic for electricity in most European countries. Some people are of the opinion that one might even equate the nuclear with the hydroelectric by assuming a coefficient of one or so.

But should not the question of savings be posed not solely in terms of energy and raw materials but above all in terms of

outflow of foreign currency, especially in the case of the countries with an adverse trade balance? This would be eminently suitable, as naturally not all sources of primary energy have the same value in foreign currency. The comparison will always appear critical, and at least to begin with, will not be taken into account very often. But not doing so is liable to render the advantages of the electro-nuclear solution less obvious to some people.

IJonetheless, striving after the optimum use of energy and raw materials must, for some time at least, be the central preoccupation of citizens and Industrialists. This in many cases may lead to seeking a combination of several energy sources--or more often, of several forms of utilizing a given form of fuel--each being used in its optimum range of efficiency. Let us again take the reheating of the steel billets before forming as an example: immersed in high- temperature gases, the colder the billets are, the more heat they absorb in a given time; and however great may be the flow of hot gases, billets cannot get hotter than gases are. Certainly there are other panameters to contend with, but this simplified approach will serve as reminder of the fact that the efficiency of a flame

furnace is lower if the billets are hot. In current operation, the average efficiency equals that observed somewhere around 700 0 C.

As regards the efficiency of the electric process, induction heating is virtually independent of temperature. Losses by

radiation increase with temperature, bug there is a better pene- tration of the induction in the metal above the Curie point, namely above 7 0 0 ~ ~ . There would therefore be a saving in primary energy if one used a flame furnace, or oven, up to about 7 0 0 ~ ~ ~ and an induction furnace above this.

This kind of duplication is costly if the energy sources are as different as flame is from electricity. But in most cases a good energy balance will be obtained by combining many electrical processes, as for instance de-freezing, or drying, by coordinated use of radiation and heat pumps. No particular technical or financial problem will generally arise from such simultaneous installations.

To conclude, it is necessary to underscore the great care to be taken in intricate comparisons between a number of disparate processes, already developed or to be developed; to be emphasized too is the imagination that will be required from now on in order to introduce new industrial processes based on electricity.

It would go against the interests of the industrialized nations (and those of their industrialists) not to attempt to rise above the partial viewpoints to which they may have hitherto adhered. We have to opt from among a lot of scarcities: primary energy,

raw materials, foreign currency. We must not focus, even temporarily, solely on savings in primary energy.

In fact, if prices of energy and raw materials properly re- flected their true cost for a nation, the minimization of the dis- counted overall cost (investment plus operation plus maintenance) of the entire sequence of processes required for turning out the finished product would not be a debatable criterion. Is it valid to assume that true costs have been found again in Europe, after the disruption of the last months? It might be hazardous to affirm it, but this will come--perhaps soon. Meanwhile it is difficult to find a simple criterion not open to criticism.

The few examples selected here from a wide choice have shown that our legitimate striving to save primary energy and raw materials may already now be satisfied through the use of our available sources of electricity, the more so if such electricity may quickly and

mainly be obtained from nuclear sources, or at least independently of hydrocarbon imports, whether liquid or gaseous.

But will industrialists worry about energy saving, and will they attune their investments to such a need? It scarcely seems likely that they will do so out of pure patriotism. There must be some financial incentive. This means that if we wish to achieve savings in energy and raw materials, we must show the industrialists not only the technical feasibility and reliability of the electrical appliances, but also the profitability of the processes and

equipment we recommend for the purpose. This implies that we must be able to turn out mass produced equipment within a short time.

Furthermore, since speed is essential, this should foster inter- national collaboration through an interchange of information among the various producers of electrical energy, manufacturers of equip- ment, and end-users. Undoubtedly, public authorities in the various countries should strive to induce innovative research on electrical processes.

D i s c u s s i o n Sweeney

The p r e s e n t a t i o n o f Bouchet, Lencz, and Mount a t t e m p t e d t o e s t i m a t e t h e demand f o r one f u e l o u t s i d e o f t h e c o n t e x t o f t h e demands f o r o t h e r f u e l s . T h i s o f c o u r s e i s c o n s i s t e n t w i t h most o f t h e work t h a t h a s gone on i n t h e p a s t , where o n e s t u d i e s t h e demand f o r e l e c t r i c i t y o r f o r n a t u r a l g a s . I t s t r i k e s me t h a t s i n c e a l l o f t h e s e f u e l s a r e c l o s e s u b s t i t u t e s , i t i s v e r y d i f f i c u l t t o e s t i m a t e t h e demand f o r e l e c t r i c i t y w i t h o u t

f o c u s i n g on n a t u r a l g a s and p e t r o l e u m o r c o a l a s s u b s t i t u t e p r o d u c t s . Of c o u r s e , one way t o d o t h i s i s t o u s e p r i c e s o r o t h e r c h a r a c t e r i s t i c s o f t h e s u b s t i t u t e f u e l a s i n d e p e n d e n t v a r i a b l e s i n t h e e c o n o m e t r i c a n a l y s i s , b u t a g a i n some o f t h e work g o i n g on i n t h e US F e d e r a l Energy A d m i n i s t a t i o n s u g g e s t s t o u s t h a t t h i s a p p r o a c h c a n b e m i s l e a d i n g .

One o f t h e t h i n g s we found i s t h a t i t i s f a i r l y e a s y t o

" e s t i m a t e " t h e demand f u n c t i o n f o r any o n e f u e l . The r e s e a r c h e r h a s a g r e a t d e a l of l a t i t u d e i n c h o o s i n g f u n c t i o n a l f o r m s ,

i n d e p e n d e n t v a r i a b l e s and s o f o r t h . However, we a l s o found t h a t a s s o o n a s one s t a r t s e s t i m a t i n g t h e demand f o r a f u e l i n con- j u n c t i o n w i t h o t h e r demands one r u n s i n t o some v e r y d i f f i c u l t problems and o f t e n d i s c o v e r s some t h i n g s wrong w i t h t h e s i n g l e - f u e l e s t i m a t e s . While I am n o t s u g g e s t i n g t h a t t h e r e n e c e s - s a r i l y a r e m a j o r d i f f i c u l t i e s w i t h t h e s t u d i e s p r e s e n t e d h e r e , I am s u g g e s t i n g t h e s e demand s t u d i e s m i g h t u s e f u l l y b e p l a c e d i n a c o n t e x t o f o t h e r f u e l demands.

I n B o u c h e t ' s p a p e r i t s t r u c k me t h a t h e i s c o r r e c t i n t r y i n g t o s t r u g g l e w i t h t h e n o t i o n t h a t you must l o o k a t combi- n a t i o n s o f v a r i o u s e n e r g y i n p u t s r a t h e r t h a n t r y i n g t o t r a n s l a t e e v e r y t h i n g t o BTU's and t o s i m p l y a g g r e g a t e t o BTU's o f i n p u t . However, a problem a r i s e s when o n e assumes t h a t p r i c e s a r e n o t c o r r e c t b e c a u s e t h e p r i c e s y s t e m c a n no l o n g e r b e u s e d f o r

aggregating inputs. I would have liked to see some discussion in that paper of how, since prices are rejected as aggregators, one goes about aggregating various inputs.

Waverman

This morning we have been told we are artists and not scientists and so I will not let Sweeney's remarks dissuade me from repeating some of the things he said to prove to you it is really science and not art. In Bouchet's paper I liked the first part very much; it reminds us that we must think in terms of output BTU's not input BTU's. If we consider effi- ciencies in transmission and conversion to final demand it is not necessarily true that electricity is the most inefficient of all fuels. Bouchet also tried to persuade us by giving us an implied social objective function which says that unless you

Im Dokument Proceedings of the Workshop on Energy Demand (Seite 129-153)